Energy storage technology is attracting more and more attention in recent years. As the applicability of energy storage technology is extending to mobile phones, camcorders, notebook PCs and even electric automobiles, there is a growing demand for high energy-density batteries as power sources for such electronic devices. Under these circumstances, lithium secondary batteries are considered as the most promising batteries and research on lithium secondary batteries is being actively undertaken.
A typical lithium secondary battery includes an anode, a cathode and a non-aqueous electrolyte solution to provide channels through which lithium ions migrate between the two electrodes, and produces electrical energy by redox reactions occurring when the lithium ions are intercalated into and deintercalated from the cathode and the anode. Such secondary batteries are currently in the spotlight due to their higher operating voltages and much higher energy densities than conventional batteries, such as Ni-MH, Ni—Cd, sulfuric acid-lead batteries. However, the performance of lithium secondary batteries is deteriorated by repeated charge/discharge cycles, which is a problem. This problem becomes more serious as the capacity density of batteries increases.
In order to solve the above problems, proposals have been made for forming solid electrolyte interface (SEI) films by adding a variety of compounds to non-aqueous electrolyte solutions. For example, Japanese Unexamined Patent Publication No. 1996-45545 discloses a method for forming SEI film using vinylene carbonate (VC). However, it is known that this SEI film has a slightly high resistance and tend to collapse at high temperature.
Thus, research is continuing on non-aqueous electrolyte solutions that form stable SEI films and are optimized for lithium secondary batteries with markedly improved cycle life characteristics.